Electrostatic reproducer for talking machines and the like



June 30, 1925. 1,544,00l

' w. GROENEBAUM ELECTROSTATIC REPRODUCER FOR TALKING MACHINES AND THE LIKE Filed Jan. 5, 1925 Patented June 30, 1925.

UNITED STATES PATENT OFFICE.

W'ILHELM GBOENEBAUM, OF NEU-BABELSBERG, NEAE BEBLIN, GERMANY, ASSIGNOB TO THE FIERI NAAMLOOZE VENNOOTSCHAP FINANCIEELE MAATSCEAPPIJ' DBIE- BEBGEN, OI' AMSTEBDAM, NETEERLANDS.

ELECTBOSTATIC BCEPBODUCEB FOR TALKING MACHINFB AND THE LIKE.

Application filed January 8, 1925. Serial No. 327.

To all whom it may concem:

Be it known that I, WILHELM GROENE- BAUM, residing at Neu-Babelsberg, near Berlin, Germany, have invented certain new and useful Improvements in Electrostatic Reproducers for Talking Machines and the like, of which the following is a specification. i

This invention relates to electrostatic reproducers for talking machines and similar apparatus.

In the usual Construction of electrostatic sound boxes or reproducers, a variable condenser of the multplate type is used, having a plurality of rigid metal plates connected together in spaced relation and a like number of similar plates connected together in such manner that the plates of each set alternate one above the other. These lates are insulated from each other either y au air gap or by sheets of a suitable dielectric material. To vary the capacit of the condenser, one set of plates is rigdly attached to an insulated support, and the other set is mounted to vary the air gap between adjacent plates.

The aforedescribed arrangement and the fact that the gaps between the movable and fixed lates must be made as small as possible, wthont establishing a metallic contact, in order to obtain a high capacity, render it necessary to exercise great care in the making of the parts and in assembling them.

An object of the present invention is to provide a nove] electrostatic reproducer for talking machine.

Another object is to provide a reproducer comprising a Variable condenser and a recording stylus or needle.

A further object is to provide an improved variable condenser consisting of plates of metallic foil separated by an elastic dielectric.

The invention is illustrated by way of example in the drawing which shows a reproducer in section.

The two sets of condenser plates each consist of lim sheets of foil. F, for example aluminum foi stacked in the same way as in an ordinary paper condenser. That is to say, the sheets of the one set alternate with the sheets of the other. In distinction from known arrangements, however, the sheets are stacked loosely, so that they can easily be pressed together by a reproducing Stylus N which is operatively connected in any approved manner with a rigid plate P. A dielectric S is interposed between the adjacent plates F of the condenser in the form of comparatively thick sheets of elastic material, such as rubber and an additional sheet is interposed between the outside plates and both the support G and the Stylus plate P. Each set of plates is provided with extension members which are adapted to be secured to a terminal connection M for supporting the plates in Suspended relation to the support G and to serve as a means for electrically connectin the plates of each set together in paralel relation and to a common terminal M. The force that returns the reproducing Stylus N to its normal position at each relaxation of its pressure is supplied by the elasticity of the sheets S which form the dielectric between the metallic foils F.

In operation, when the reproducing stylus N is set in vibrating motion, by following the groove on a record (not shown) of a phonograph for example, this motion is transmitted to the plate P in contact with the condenser. on the condenser plates F and interposed dielectric sheets S, caused by the up and down movement of the stylus, are suflicient to move the said plates toward and away from each other by virtue of the elasticity of the dielectric, thus varying the capacity of the condenser. If the terminals M of the deVice are connected in circuit with a source of electrical energy and a telephone receiver or similar apparatus, the variations in the Capacity of the condenser will cause variations in the current flowing through the receiver. The receiver will then reproduce the sound waves recorded on the record of the talking machine without the distortion inherent in the diaphragm of the mechanical reproducer.

I claim 1. A reproducing device of the kind described, comprisin a stuck of two sets of thin substantially %imp metallic sheets, the

sheets of one set being placed between the.

sheets of the other set, elastic insulating sheets interposed between adjacent metallic sheets, insulating means at the ends of the stack, a support, terminals mounted on said The variations in pressure' sheets, a support carrying terminals, means for loosely suspending the respective sets of sheets to said terminals, and a Stylus asso- 15 ciated with said stack whereby movement of the Stylus varies the Capacity of said device. In testimony whereof I have aflixed my signature in presence of two witnesses.

WILHELM GROENEBAUM.

VVitnesses E. WVURM, L. HERBST. 

